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PubMed1979

Separation of human lymphocytes and monocytes by velocity sedimentation at unit gravity.

An improved method of separating human peripheral blood lymphocytes and monocytes by velocity sedimentation at unit gravity is described. Cell separation capacity is considerably increased, while the time required for optimal separation is markedly reduced. Simple devices make it possible to layer and fractionate the gradients within 15 min. Overall recovery is 85%. On a small scale, monocytes were isolated greater than 80% pure from 4--20 X 10(7) mononuclear leukocytes. The average yield was 40% of all monocytes recovered after fractionation. In the same sedimentation runs 60% of all recovered lymphocytes were obtained strongly depleted of monocytes (monocyte contamination less than 0.2%). On a large scale 3--6 X 10(8) monocytes with an average purity of 85% were isolated from 3--6 X 10(9) mononuclear leukocytes in 2 subsequent runs. All cells recovered from the gradient were functionally active according to rosette formation, phagocytosis, stimulation by mitogens and in cytotoxicity tests.

Cell Differentiation↗

PubMed1982

Rapid large scale fractionation of lymphoid cells by velocity sedimentation at unit gravity, using Percoll as separation medium.

Available methods for separation of cells by velocity sedimentation at unit gravity allow a maximum cell load of 2 x 108 lymphoid cells. Here we describe a method, based on the 'tilting' procedure of Bont et al. (1979), which allows separation of up to 4.5 x 109 lymphoid cells, while retaining full separation and rapidity. Percoll instead of Ficoll was used as gradient medium. The relationship between cell sedimentation velocity and cell volume was analyzed by two different methods, i.e., electronic cell sizing and diameter measurements of cytocentrifuged cells.

Animals↗

PubMed1983

Separation of lymphocyte subsets by expanding velocity sedimentation of E-rosettes at unit gravity.

An expanding velocity sedimentation procedure at unit gravity has been used to separate human lymphocyte subsets on the basis of E-rosette formation. It is shown that the method allows gentle yet efficient separation of T and non-T lymphocytes in a continuous gradient of colloidal silica (Percoll). Less efficient separation was obtained in gradients consisting of polymerized sucrose (Ficoll 70). The technique offers a special advantage in the possibility of separating lymphocytes binding differing numbers of indicator red cells. The method should be generally adaptable to various rosetting techniques, including systems where the indicator cells are attached with weak bonds. As judged by vital staining, the lymphocytes are in excellent condition after the separation.

Animals↗

PubMed1988

Effects of gravity on regional and capillary blood flows in the human toe.

The purpose of this study was to investigate the relative effects of gravity on capillary and regional blood flows in human extremities. Eighteen male subjects 20 to 40 years of age consented to have capillary blood cell velocity (CBV) measured in nailfold vessels of the large toe via video densitometry, and to have total blood flow (TBF) to the toe measured via plethysmography. These measurements were made first with the foot at heart level (HL), then after the foot had been lowered an average of 56 cm below the heart (BH). In the HL position CBV and TBF averaged respectively 0.26 mm/sec and 2.0 ml/min/100 ml. Lowering the foot elicited a decrease in CBV in all vessels studied (P less than or equal to 0.001). Average CBV in the BH position was 0.11 mm/sec. By contrast TBF on the average increased to 2.9 ml/min/100 ml in the BH position (P less than or equal to 0.05). However, this was not a consistent finding since both increases and decreases in TBF were observed among the individual subjects. These results indicate that the immediate precapillary vessels in the cutaneous circulation of the toe will consistently vasoconstrict when the foot is placed in a dependent position. However, the net effect on vessels governing regional flow in this area, e.g., A-V shunts, appears to result from a competition between dilator and constrictor influences. The overall result of these adjustments is that during orthostasis blood is shifted away from the superficial capillaries of the lower extremities. The relevance of this to blood-tissue fluid balance is discussed.

Adult↗

PubMed1987

Gravity-induced hyperventilation is caused by a reduced brain perfusion.

The suggestion that hyperventilation caused by increased gravity is mediated by a decrease in brain perfusion has led us to propose a mathematical model based on: (1) the CO2 balance equation for the respiratory center (RC), and (2) the relationship between RC blood flow (QRC), foot-to-head acceleration (Gz) and PRCCO2, namely, QRC = [1 - a(Gz - 1)](b X PRCCO2 + c), where the coefficients a, b and c can be calculated from data in the literature. QRC is significantly affected by + GZ only at high PaCO2. The model can be used to calculate oxygen pressure in the RC; the numbers so obtained are in good agreement with measurements of jugular vein PO2 obtained by others.

Blood Flow Velocity↗

PubMed1989

The role of location probability in the programming of saccades: implications for "center-of-gravity" tendencies.

Short-latency saccades to targets among nontarget backgrounds are often directed to the center of the entire (target + nontarget) stimulus configuration. This "averaging" or "center-of-gravity" tendency has been attributed to an automatic, reflexive saccadic response to a poorly-resolved visual signal. We investigated the role of high-level processes by varying the probability of the target appearing in one of two locations. Subjects were asked to make a saccade to a target "+" located above-right or above-left of a central fixation point. A nontarget ("x") was in the other location (directional separation = 30 deg). The mean latencies were short (180-230 msec) in accordance with instructions. Mean saccadic direction was shifted to the right by 24-52% of the directional separation of the stimulus pair as the probability of the target appearing on the right increased from 0.2 to 0.8. The difference in saccadic directions as a function of the actual target location was small and independent of probability, showing that probability introduced a bias without affecting the discriminability of the target from the nontarget. The effect of probability was reduced when the discrimination of the target from the nontarget was easier (square vs triangle), and abolished (saccadic accuracy near perfect with the same average latencies) when the target was presented alone. The results show that the direction of short-latency saccades, initiated before the target has been distinguished from a nearby nontarget, is based on the prior history of target locations and expectations about the future location of the target. High-level plans can account for effects of nontargets on saccades. To infer that a reflexive sensorimotor averaging mechanism exists solely on the basis of observed saccadic "centering" tendencies is unwarranted.

Eye Movements↗

PubMed1989

Visually perceived eye level and perceived elevation of objects: linearly additive influences from visual field pitch and from gravity.

Observing a pitched visual field (i.e. tilted around a horizontal axis in the observer's frontal plane) results in large changes in the elevation visually perceived to correspond to eye level (VPEL) and in the perceived elevation and size of stationary objects viewed against the field. With topforward pitch (top toward observer) VPEL lies above true eye level and objects appear smaller and lower; with topbackward pitch VPEL lies below true eye level and objects appear larger and higher. Oscillation of the pitched field induces synchronous perceived oscillation of elevation of a stationary target viewed against the field. Typical VPEL settings deviated from true eye level by 20 degrees with the field pitched at 40 degrees, although some individuals mislocalized by as much as 40 degrees. VPEL varied linearly with visual field pitch with individual slopes for the relation between VPEL and visual field pitch ranging from +0.42 to +0.78 (avg = +0.56). The linear correlation (r) between VPEL in darkness and against an erect visual field was +0.91. The two relations--VPEL vs visual field pitch, VPEL in darkness vs VPEL in the erect illuminated visual field (slope approximately equal to 0.5)--are both accurately predicted by the linear model: VPEL = kvV + kbB; in which V is the influence of visual field structure and B is the influence of the body-referenced mechanism which combines information regarding the orientation of the head relative to gravity, the position of the eye in the orbit, and the vertical location of the image on the retina; kv and kb are the relative weights of V and B with kv + kb = 1. In an illuminated field kv = kb approximately equal to 0.5; in the dark kv = 0, kb = 1.

Gravitation↗

PubMed1994

The influence of gravity on Donders' law for head movements.

Three-dimensional (3-D) head rotations were examined in seven human subjects when their bodies were inclined +/- 45 degrees in pitch and roll. The selection of 3-D orientations of the head while subjects looked at visual targets was similar to that seen previously for the eye: there was a small static counter pitch and counter roll of approx. 10%. Thus rotations of the head relative to the trunk are largely independent of the trunk's position relative to gravity and the head's torsional orientation is primarily dependent on its horizontal and vertical position relative to the trunk.

Eye Movements↗

PubMed1996

The 'center of gravity' of words: evidence for an effect of the word-initial letters.

When the eye saccades to eccentric word targets, it tends to land in a position which can be described as the center of gravity of the configuration. By manipulating the relative intensity of the word-initial and -ending letters, it was shown that the 'global effect' of luminance distribution within words is strongly attenuated when the word-initial letters are informative and orthographically irregular. Results show that the orthographic structure of the word-initial letters exerts an influence on the saccadic computation that may cancel the luminance distribution effect.

Fixation, Ocular↗

PubMed1993

Shunted hydrocephalus: normal upright ICP by CSF gravity-flow control. A clinical study in young adults.

Hydrocephalic patients with years of ventricle shunts may be disabled by shunt overdrainage. Gravity-induced upright CSF shunt flow produces this overdrainage with abnormally low, upright ICP. Consequently, the concept of a normal level of zero ICP, which ventricle shunts must mimic, was developed. For 4.5 years, this concept has been applied in hydrocephalus patients by using a Siphon Control Device as a Zero Pressure Device in ventricle shunts. The results in 56 patients, including 42 overdrainage problems, were assessed by clinical grading, ICP record analyses, and computed tomographic (CT) ventricle size comparisons. All patients ultimately achieved satisfactory clinical results. This occurred in 80% of the patients on the first insertion. Adjustment of the vertical level of the Zero Pressure Device was necessary in 20%. The optimum clinical result correlated with an upright ICP of -66 mm of H2O. This postoperative ICP correlated within 4 mm of the Zero Pressure Device placement below vertex. Ventricle size correlated poorly with clinical grade and normal ICP. Only 73% of slit ventricles enlarged by 16.5 months. The need to mimic normal upright ICP by maintaining a normal level of zero upright ICP in shunted patients is supported by these results.

Adolescent↗

PubMedDate not supplied

Subgravity states: key to understanding the role of terrestrial gravity in human behaviour.

The early orbital flights, although undertaken with considerable confidence, involved some uncertainty because of the impossibility of simulating under terrestrial conditions all of the conditions encountered in space. However, space-flight achievements by both the American astronauts and Soviet cosmonauts have firmly established that man, if appropriately selected, trained, and protected by suitable life-support systems, can perform efficiently for long periods of time in the hostile environment of space. We know that the side effects of vestibular origin pose important problems in space exploration, and the neurophysiological effects of any extensive, rapid adaptation processes in subgravity states have enabled a better understanding of man's compensatory capabilities. With the successful establishment of orbiting research laboratories, an unparalleled opportunity exists that will undoubtedly enable better understanding of the role played by gravity in normal terrestrial activity, not only as it affects our vestibular physiology, but also as it may or may not concern other systems and at different organizational levels in the body.

Acceleration↗

PubMedDate not supplied

Early cardiovascular adaptation to zero gravity simulated by head-down tilt.

The early cardiovascular adaptation to zero gravity, simulated by head-down tilt at 5 degrees, was studied in a series of 10 normal young men. The validity of the model was confirmed by comparing the results with data from Apollo and Skylab flights. Tilt produced a significant central fluid shift with a transient increase in central venous pressure, later followed by an increase in left ventricular size without changes in cardiac output, arterial pressure, or contractile state. The hemodynamic changes were transient with a nearly complete return to the control state within 6 hr. The adaptation included a diuresis and a decrease in blood volume, associated with ADH, renin and aldosterone inhibition.

Adaptation, Physiological↗

PubMed1980

Device for mass measurement under zero-gravity conditions.

The problem considered in this paper is the investigation of the properties of a mass-meter, i.e. the device for determining the mass of cosmonaut's body under zero-gravity conditions. The estimates of accuracy of mass measurement by this device are given, and the results of measuring the masses of cosmonauts' bodies on the Salyut 5 and 6 orbital stations are presented.

Aerospace Medicine↗

PubMed1994

Cardiovascular responses to KC-135 hyper-gravity.

The present study was designed with two intentions; Are the effects of angular velocity detectable in the cardiovascular responses during the hyper-G? Another is object to examine how the otolith signal could modify the cardiovascular responses provoked by the exposure to the hyper-G. NASA/KC-135 hyper-gravity flight was used to generate high gravito-inertial forces to exclude a possible effect of angular velocity. Six healthy subjects was indicated to make dorsal flexion of the neck to reduce the otolith input. An exposure to +l.8Gz stress resulted in a remarkable increase of systolic and diastolic blood pressure, thereby pulse pressure became a little bit narrower. R-R interval revealed a tachycardia during the hyper-G except one subject. The present experiment bore the similar cardiovascular responses as those observed in the previous studies with a short rotating radius, suggesting that almost no effect of angular velocity acts on their responses. A weaker otolith input could possibly work on them. However a systematical observation can not recognize among the subjects for the vestibular effect on the cardiovascular responses. This fact of vestibular qualification leads us to speculate that it would depend on the subjects or other factors.

Adult↗

PubMed1980

Gravity sedimentation analysis of human blood leukocytes.

A new method of sedimentation analysis of human blood leukocytes is described. Platelets, lymphocytes, monocytes, and polymorphonuclear cells isolated from normal human peripheral blood have been analyzed alone and in mixture by gravity sedimentation, employing a computerized scanning instrument. All four classes could be clearly resolved from each other exhibiting sedimentation velocities of 0.06 +/- 0.00, 1.04 +/- 0.11, 1.27 +/- 0.15 and 1.89 +/- 0.21 x 10(-4) cm/s, respectively, at 37 degrees C in a 2.5--6.25% Ficoll gradient in Medium 199. Less than 10(6) cells can be used for analysis. Possible applications of the method are discussed.

Blood Platelets↗

PubMed1996

Influence of the initial projection of the centre of gravity on posturo-kinetic coordination in humans. Application from a horizontal quadrupedal stance during voluntary limb raising.

The purpose of the study is to investigate the influence of initial projection of the centre of gravity (CG) on the spatial and temporal organization of the dynamic phenomena accompanying a voluntary movement in humans. From a horizontal quadrupedal stance, ten normal subjects were instructed to raise the right forelimb towards a support target in self paced velocity conditions. Three experimental conditions were tested for which the initial CG projection was either within (C1), at the limits of (C2) or outside the supporting triangle (C3). The results showed that vertical force variations on the four supports always preceded the first vertical displacement of the right wrist (onset of the movement). From C1 to C3, the duration of these anticipatory dynamic phenomena increased enabling an adjustment of the CG position such that equilibrium constraints were fulfilled. For all conditions, the acceleration peak of the CG occurred prior to the onset of movement and from C1 to C3, its magnitude increased in a single direction of the horizontal plane. For each condition, the load transfer was directed to the left forelimb and the right hindlimb (diagonal strategy) and reached a maximal value at the time of lift-off. With respect to this moment, the onset of the movement occurred increasingly early from C1 to C3. These results suggest that contribution of peripheral cues to postural control is more important, when the requirements of horizontal CG displacement increase.

Adult↗

PubMed1996

Feeding frequency affects cultured rat pituitary cells in low gravity.

In this report, we describe the results of a rat pituitary cell culture experiment done on STS-65 in which the effect of cell feeding on the release of the six anterior pituitary hormones was studied. We found complex microgravity-related interactions between the frequency of cell feeding and the quantity and quality (i.e. biological activity) of some of the six hormones released in flight. Analyses of growth hormone (GH) released from cells into culture media on different mission days using gel filtration and ion exchange chromatography yielded qualitatively similar results between ground and flight samples. Lack of cell feeding resulted in extensive cell clumping in flight (but not ground) cultures. Vigorous fibroblast growth occurred in both ground and flight cultures fed 4 times. These results are interpreted within the context of autocrine and/or paracrine feedback interactions. Finally, the payload specialist successfully prepared a fresh trypsin solution in microgravity, detached the cells from their surface and reinserted them back into the culture chamber. These cells reattached and continued to release hormone in microgravity. In summary, this experiment shows that pituitary cells are microgravity sensitive and that coupled operations routinely associated with laboratory cell culture can also be accomplished in low gravity.

Adrenocorticotropic Hormone↗

PubMed1990

Actin filaments responsible for the location of the nucleus in the lentil statocyte are sensitive to gravity.

The location of the nucleus in statocytes or lentil roots grown: 1), at 1 g on the ground, 2), on a 1 g centrifuge in space, 3), in simulated microgravity on a slowly rotating clinostat (0.9 rmp) 4), in microgravity in space was investigated and statistically evaluated. In cells differentiated at 1 g on the ground, the nuclear membrane was almost in contact with the plasmalemma lining the proximal cell wall, whereas in statocytes of roots crown on the clinostat there was a distance of 0.47 micrometers (horizontal clinorotation) and or 0.76 micrometers (vertical clinorotation) between these membranes. However, in microgravity the nucleus was the most displaced, 0.87 micrometers from the proximal cell wall. Centrifugation of vertically grown roots in the root-tip direction showed that the threshold of centrifugal force to detach all nuclei from the proximal cell wall was about 40 g. In statocytes developed in the presence of cytochalasin B at 1 g the nuclei were sedimented on the amyloplasts at the distal cell pole, demonstrating that the location of the nucleus depends on actin filaments. The results obtained are in agreement with the hypothesis that gravity causes a tension of actin filaments and that this part of the cytoskeleton undergoes a relaxation in microgravity.

Actins↗